1. Field of the Invention
The present invention relates in general to controlling tracking in slow mode playback of a video cassette recorder (VCR), and more particularly to an apparatus and a method for controlling tracking in a slow mode playback in which a tracking error is automatically controlled when it generates a noise on a screen in the slow mode playback, so that an optimal picture state can be obtained.
2. Description of the Prior Art
Generally, a video signal is recorded on the tracks of a magnetic tape by a magnetic head and the recorded video signal is played back as the tracks of the magnetic tape are traced by the magnetic head. At this time, the tracks of the magnetic tape must accurately be traced by the magnetic head, which is called tracking.
Referring to FIG. 1, there is shown a block diagram of a conventional apparatus for controlling tracking in a slow mode playback. As shown in this drawing, the conventional tracking control apparatus comprises a video head 1 for detecting a video signal recorded on a magnetic tape, a pre-amplifier 2 for amplifying the detected video signal from the video head 1 by a predetermined level, an envelope detector 3 for converting an output signal from the pre-amplifier 2 into a direct current (DC) voltage and outputting the converted DC voltage to a microcomputer 5, and a manual tracking controller 4 for outputting a tracking control signal to the microcomputer 5 in response to a key input signal from the user.
The microcomputer 5 is adapted to output a servo control signal in response to the DC voltage from the envelope detector 3 and the tracking control signal from the manual tracking controller 4.
The conventional tracking control apparatus also comprises a servo device 6 for outputting a capstan phase control signal in response to the servo control signal from the microcomputer 5, and a capstan motor 7 for driving a capstan in response to the capstan phase control signal from the servo device 6.
The conventional tracking control apparatus with the above-mentioned construction is adapted to play back the video signal recorded on the magnetic tape in a slow mode by repeatedly performing normal-speed playback--still playback--normal-speed playback--still playback, as will hereinafter be described in detail with reference to. FIGS. 5A to 5D, which are waveform diagrams of the signals from the components shown in FIG. 1.
First, upon receiving the capstan phase control signal from the servo device 6 as shown in FIG. 5A, the capstan motor 7 performs repeatedly an acceleration traveling (interval A in FIG. 5A), a normal-speed traveling (interval B in FIG. 5A) and a deceleration traveling (interval C in FIG. 5A). At this time, the video head 1 traces the magnetic tape as shown in FIG. 2. In FIG. 2, the playback enters from the still mode into the normal-speed mode in an interval A. The normal-speed playback is performed in an interval B. The playback is changed from the normal-speed mode to the still mode in an interval C. The still playback is performed in an interval D. In this manner, the video signal recorded on the magnetic tape is detected by the video head 1 as shown in FIG. 5D and then applied to the pre-amplifier 2. The pre-amplifier 2 amplifies the detected video signal from the video head 1 by the predetermined level and outputs the amplified video signal to the envelope detector 3. The envelope detector 3 detects an envelope of the amplified video signal from the pre-amplifier 2 as shown in FIG. 5C. Then, the envelope detector 3 converts the detected envelope into the DC voltage and outputs the converted DC voltage to the microcomputer 5. Here, a head switching signal, as shown in FIG. 5B, is a reference signal of the system.
The microcomputer 5 outputs the servo control signal to the servo device 6 in response to the DC voltage from the envelope detector 3. The servo device 6 outputs the capstan phase control signal to the capstan motor 7 in response to the servo control signal from the microcomputer 5 to control a phase of the capstan motor 7, so as to make the tracking accurate.
On the other hand, in the case where a noise is generated on the screen in the slow mode playback, the user applies a control signal to the manual tracking controller 4 using a remote controller (not shown). The manual tracking controller 4 outputs the tracking control signal to the microcomputer 5 in response to the control signal from the user. Upon receiving the tracking control signal from the manual tracking controller 4, the microcomputer 5 outputs the resultant servo control signal to the servo device 6, thereby causing the tracking to be controlled.
However, in the above-mentioned conventional tracking control apparatus, the capstan phase control signal which is applied to the capstan motor 7 in the slow mode playback is controlled as shown in FIG. 5A by a predetermined program of the microcomputer 5. For this reason, the user must manually control the tracking using a tracking control key when a noise is generated of the noise on the screen. This causes an inconvenience to the user.